淡水水体溶解有机氮对有毒藻种的生物有效性

溶解有机氮(Dissolved organic nitrogen,DON)是多数天然水体中溶解氮的主要组成部分。天然水体DON是许多微生命体包括有毒藻种的氮营养源,在供水安全以及水体富营养化等方面的生态环境效应不容忽视。文章系统地介绍了淡水水体DON含量与来源、生物有效性与估算方法,以及对有毒藻种生长的影响。DON的来源是影响水体中DON含量动态特征的关键因素。DON来源包括陆地径流,植物碎屑,土壤淋溶液,沉积物释放,大气沉降,藻类、大型植物、细菌与细胞死亡或自我分解,微型及大型浮游动物捕食和排泄、分泌物释放等。研究表明约有12%～72%的DON可迅速被生物所利用,具显著差异,究其原因可能是其来源组成、化学本质(分子质量与极性)、测试生物组成、是否有细菌作用等因素造成的。不同藻种具有不同氮源利用能力,DON对藻类生长具有直接或间接的作用,并可能影响藻类群落结构(有毒藻类成为优势种)。考虑到水环境保护与饮用水安全供水的重要性,未来研究应重视淡水水体DON生物有效性与其化学本质的揭示,尤其是对有毒藻种。

Bioavailability of dissolved organic nitrogen in freshwaters to toxic algae

Dissolved organic nitrogen (DON) can be a significant component of the dissolved nitrogen pool in most of natural waters. Many species of DON can serve as N source directly or indirectly to phytoplankton and bacteria, thus affect the eutrophi-cation and the supply of safe drinking water. In this paper, the contents, sources, bioavailability and its estimation methods, as well as the effects on the growth of toxic algae, of DON in freshwaters were systematically reviewed. The quantitative and dynamic characteristics of DON in natural waters are greatly impacted by their sources which can be classified as allochthonous and autochthonous ones. The former include terrestrial runoff, leaching from plant detritus and soils into streams and rivers, sediments, and atmospheric deposition. The later include the exudation, death and autolysis of algae, macrophytoplankten, bacteria and other cells. The grazing and excretion of micro-and macrozooplankton also contributed to the later source. It was reported that 12 to 72% of the DON could be biologically utilized in days to weeks and the bioavailability showed significant differences due to their different sources, chemical nature (molucular weight and polarity), and the bioassay organisms involved. Specific DON compo-nents could exert selective pressure over phytoplankton community composition. In particular, some harmful algae species would take DON as their preferred nutrition over inorganic nitrogen, which make such algae the dominated species. As the security of source water and the protection of water environment are concerned, it is crucial to understand the bioavailability of DON in freshwaters to toxic algae and its chemical nature.